1. Field of the Invention
The present invention relates generally to an injection molding apparatus and, in particular to an adjustable valve pin actuator.
2. Background Art
In an injection molding apparatus, at least one hot runner nozzle delivers melt to a mold cavity through a mold gate. Valve pins are well known in the art for use in controlling the flow of melt through mold gates. Valve pins are often controlled by actuators, which advance or retract the valve pins either to close or open the mold gates, respectively, or to vary the flow to mold cavities.
In most valve-gated applications, a valve pin is controlled by an actuator, which advances and retracts the valve pin. Proper seating of the valve pin in the mold gate is necessary in order to prevent plastic melt from leaking or stringing and to prevent gate flash when the valve pin is advanced to shut off the flow from the melt into the mold cavity. Due to differences in the molding conditions and machining tolerances at each mold cavity, a valve pin for a particular cavity may require a longitudinal axial adjustment so that the valve pin will properly seat in the mold gate. If the valve pin is too long, an operator must remove the valve pin assembly, machine the valve pin to adjust the length, and re-insert the valve pin assembly into the machine. If the pin is still too long, the procedure must be repeated again. If the valve pin is too short, the valve pin must be replaced and subsequently machined to size. This procedure is cumbersome, time consuming, and results in lost production time for the manufacture. In addition, inserting and removing the valve pin repeatedly may cause damage to the valve pin.
Further, each valve pin is machined for a particular actuator and mold gate assembly and is not interchangeable. During regular maintenance, actuator components are disassembled and valve pins may become mixed up. Regular maintenance also often requires the dissembling of all components of an actuator including the extraction of the valve pin. In addition to the potential damage that may occur upon removing and inserting the valve pin, the valve pin length will have to be reassessed upon reassembling the actuator components. Thus, such labor intensive regular maintenance adds time and expense which is undesirable in mass production industries such as injection molding.
Another method an operator may use to adjust the axial position of the valve pin is to insert one or more spacers into a cylinder or attached to a piston to limit the course of travel of the piston. If the piston is prevented from extending the valve pin over the entire course of travel of the piston movement, it will create the effect of a shortened valve pin. Similarly, if the piston is prevented from retracting the valve pin over the course of travel of the piston, it creates the effect of a longer valve pin. While inserting spacers is easier than machining the valve pin, it is inaccurate, in that the fineness of the adjustment is limited by the thinness of the spacer. Further, the actuator must be almost entirely disassembled to insert the spacers.
Removing and reinserting a valve pin during actuator maintenance can cause damage to the valve pin. Further, when a valve pin is replaced after actuator maintenance, misalignment of the valve pin and damage may occur if it has been rotated and is not in the same rotational position as before it was removed.